Electron discharge device of the focussed-beam type



July 3, 1951 R. ADLER 2,559,037

ELECTRON DISCHARGE DEVICE OF THE FOCUSSED-BEAM TYPE Filed Dec. 30, 9 8 2 Sheets-Sheet 1 ROBERT ADLER INVENTOR.

HIS AGENT- July 3, 1951 R2. ADLER. 2,559,037

ELECTRON DISCHARGE. DEVICE OF THE F'OCUSSED-BEAM TYPE Filed Dec. 50, 1948 2 Sheets-Sheet 2 F/ga Output Voltage lnpu1 Frequencv ROBERT ADLER INVENTOR.

ms AGENT Patented July 3, 1951 ELECTRON DISCHARGE DEVICE OF THE FOCUSSED-BEAM TYPE Robert Adler, Chicago, 111., assignor to Zenith Radio Corporation, a corporation of Illinois Application December 30, 1948, Serial No. 68,285

20 Claims.

This invention relates to electron discharge devices, and more particularly, to electron discharge devices of the type which may be employed to accomplish amplitude limiting and demodulation of an angular-velocity modulated wave signal along a single electron stream.

In the copending application of Robert Adler, Serial No. 7,864, filed February 12, 1948, for Electron Discharge Devices, now Patent No. 2,511,143, issued June 13, 1950, and assigned to the same assignee as the present application, there is disclosed and claimed a novel type of electron discharge device which provides improved amplitude limiting characteristics by virtue of the step function type operating characteristic of a control grid. Such a characteristic is accomplished by locating the control grid in a position along the electron stream following an accelerating electrode having an aperture, the distance between the aperture and the control grid being greater than at least one of the transverse dimensions of the aperture.

As a preferred embodiment of the aforementioned copending application, there is disclosed and claimed a novel electron tube which is capable of functioning simultaneously as an amplitude limiter and demodulator for an angular-velocity modulated wave signal, such as a frequency modulated carrier wave. This preferred embodiment comprises, in essence two control systems cascaded along a single electron stream, each of the systems comprising an apertured accelei'ating electrode followed by a control grid. Although the amplitude limiter-frequency demodulator disclosed and claimed inthe above identified copending application is operative and affords considerable advantages over prior art arrangements, it is subject to certain structural limitations. For example, that structure may not lend itself as readily as desired to large scale production, since certain of the elements require special working.

Furthermore, since two control grids are cascaded along a single electron stream, it is essential that the electrons emerging from the first control grid retain the form of a well defined beam. At the same time, it is necessary to limit the number of electrons, rejected by the first grid when that grid is negative, which return through the aperture in the first accelerating electrode to the vicinity of the cathode to as small a proportion of the total space current as possible, since even a small number of electrons returning through the aperture may result in non-uni-.

formity of the operating characteristics of indi- Ill] vidual tubes. These two requirements are mutually contradictory; the beam should be as well focused as possible in order to be controllable by the second grid, and at the same time, as little focusing as possible should be employed between the first accelerating electrode and the first grid, so that electrons rejected by the first grid when that grid becomes negative are not refiecte l through the aperture of the first acceleratin; electrode but are collected by the solid portions 0 that electrode. The structure of the above mentioned copending application represents a compromise between these two contradictory requirements, and it has been found that while this compromise aifords substantial advantage over prior art arrangements, it is a rather critical one, and small variations in the dimensions of the tube elements of individual tubes may result in undesirable large discrepancies in the operating characteristics of such individual tubes.

It is an important object of the present invention to provide an improved electron discharge device of the general type disclosed in the aforementioned copending application, particularly suited for use as an amplitude limiter and frequency demodulator, in which the beam definition is improved, while at the same time, a reduction is effected in the number of electrons returning to the vicinity of the cathode in response to negative instantaneous potentials at the first grid.

It is another object of the invention to provide an improved electron discharge device of this type in which the electrode dimensions and spacings are less critical than those of the structure disclosed in the above identified copending application, in order to provide improved uniformity of operating characteristics of individual devices constructed on a mass production basis.

It is a further object of the invention to provide a novel electron gun having a high perveance (i. e., a high ratio of beam current to three-halves power of accelerating voltage) while providing improved beam definition.

The present invention provides an electron discharge device comprising an electron gun which includes a cathode having a substantially plane emitting surface. A focusing electrode, having an aperture disposed opposite the emitting surface of the cathode, is spaced from the cathode. An accelerating electrode is spaced from the focusing electrode on the side thereof remote from the cathode. The accelerating electrode has an aperture the boundaries of which extend toward the cathode and terminate at a predetermined distance from those boundaries of the 3 aperture of the focusing electrode which are nearest the cathode. This predetermined distance does not exceed a small fraction of the transverse dimensions of the aperture of the accelerating electrode.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may more readily be understood, however, by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like ref erence numerals indicate like elements, and in which:

Figures 1 and 2 represent schematic cross sectional views of electron discharge devices constructed in accordance with the present invention,

Figure 3 is a schematic circuit diagram of a system incorporating an electron discharge device constructed as shown in Figure 1 or Figure 2, and

Figure 4 is a graphical representation of a characteristic of the circuit of Figure 3.

With reference to Figure 1, there is shown a schematic representation of an electron discharge device having a plurality of elements disposed in substantially symmetrical relation across a common electron path, represented by center plane Ill. The electron discharge device comprises an electron gun, which includes an indirectly heated cathode ll having a substantially plane emitting surface l2, an auxiliary electrode l3, a first focusing electrode l4, and a first accelerating electrode l5. Emitting surface I2 is preferably made plane for ease of manufacture. although that surface may be made slightly convex toward first accelerating electrode [5. Auxiliary electrode I3 comprises wing portions l6 which are substantially coplanar with emitting surface l2 of cathode ll. Focusing electrode I4 is spaced from cathode I I along the electron path and has an aperture disposed opposite emitting surface i2. First accelerating electrode I is spaced from first focusing electrode M on the side thereof remote from cathode II and has an aperture ll bonded by a pair of opposed lips l8 extending toward cathode II and terminating at'a distance from those boundaries of the aperture of first focusing electrode 14 nearest cathode emitting surface I2 which does not exceed a small fraction of the transverse dimensions of aperture l1. Specifically, in the embodiment of Figure 1, cpposed lips I8 extend toward cathode II and into the aperture of first focusing electrode l4, although it is only necessary that lips l8 be spaced from those boundaries of the aperture of electrode l4 nearest cathode emitting surface 12 by an amount which does not exceed a small fraction of the width of aperture I'I.

Following first accelerating electrode IS, in the order named, are a second focusing electrode [9, a first control grid 20 having a contour substantially convex toward aperture [1, a third focusing electrode 2|, a second accelerating electrode comprising a screen grid portion 22 and a beam directing portion 23 having an aperture 24, a fourth focusing electrode 25, a second control grid 26 having a bulged central portion 21 extending toward aperture 24, and an anode 28 having a contour substantially similar to that of control grid 26. While screen grid portion 22 and beam directing portion 23 are shown to be formed as a single structural part, it is apparent that they may be separated to form two discrete structural parts; the term second accelerating electrode is to be interpreted to cover both portions, whether or not they comprise a single structural part. The electrodes are all supported Within an evacuated envelope (not shown), as by means of supporting posts 29.

Second focusing electrode l9, here shown to be of hairpin construction, defines an aperture which is large relative to aperture ll of first accelerating electrode I5. First control grid 20 may comprise a series of parallel spaced wires (for example per inch) and may be formed with a radius of curvature of about inch. Third focusing electrode 2| is shown as comprising a pair of wing portions which define an aperture of the same order of magnitude as that defined by second focusing electrode I9. Screen grid portion 22 may comprise a series of parallel spaced wires (for example 68 per inch) preferably having a radius of curvature substantially the same as that of the grid wires of first control grid 23. Beam directing portion 23 has a central aperture 24 which is larger than aperture ll of first accelerating electrode Hi. The structure of fourth focusing electrode 25, second control grid 26, and anode 28 is described and claimed in the copending application of Robert Adler, Serial No. 15,713, filed Ma 18, 1948, for Electron Discharge Devices, which application is assigned to the same assignee as the present one.

The elements preferably have substantial length in the direction perpendicular to the plane of the paper, so that the electron beam assumes the form of a wedge or sheet of substantially rectangular cross section, For example, the length of the elements in the direction perpendicular to the plane of the paper may be many times the width of the electron stream. With such a configuration, the apertures I! and 24 of the first and second accelerating electrodes, respectively, and the apertures of focusing electrodes l4, 19, 2|, and 25 may be accurately defined as slots, and the term slot as used in the appended claims, is intended to be restrictive to a configuration of this type. It is, however, contemplated that other configurations may be advantageously employed. For example, the apertures of the respective electrodes may be round, in which event a circular cross section beam is produced. The term aperture," as used in the appended claims, is intended to be inclusive of such alternative configurations as well as of the preferred slotted construction.

In operation, cathode II is energized, as for example by means of a heater (not shown), and electrons are emitted from emitting surface l2 in the form of a thin sheet-like beam of rectangular cross section. Auxiliary electrode I3 and first focusing electrode 14 are maintained at or near cathode potential, and first accelerating electrode I5 is maintained at a predetermined positive unidirectional potential. The resulting electrostatic field set up in the region between emitting surface l2 and aperture I! is such that electrons originating at surface [2 are formed into a beam which is originally divergent but upon approaching lips l8, the electrons encounter a strongly convergent field and are focused upon leaving aperture l'l. Because the beam is originally divergent, the beam definition is considerably better than that obtainable with conventional types of electron guns employing electron beams which are initially either convergent or substantially parallel.

First control grid 20 is disposed beyond aperture I! at a distance greater than at least one of the transverse dimensions (for example, the.

width or distance between lips I8) of that aperture. In this manner, the characteristic of beam current through control grid 20 versus the voltage applied to that grid is made to resemble a step function, having two regions of substantially zero transconductance separated by a narrow region of high transconductance. The reasons that such a characteristic is obtained are explained fully in copending application Serial No. 7,864. Second focusing electrode I9, which may be maintained at the same potential as first focusing electrode I4, serves to aid the focusing of the beam impinging on first control grid 20, and the electron gun. second focusing electrode l9, and first control grid 20 are so arranged relative to each other that the convergent beam emerging from aperture I'I intercepts a narrow central portion of control grid 20.

Third focusing electrode 2I and screen grid portion 22 of the second accelerating electrode constitute a convergent electron lens, the purpose of which is to refocus the electron beam emerging from first control grid 20. Third focusing electrode 2I may be operated at the same potential as first and second focusing electrodes I4 and I9. Screen grid portion 22 may be operated at the same potential as first accelerating electrode I5 and has a contour substantially similar to that of first control grid 20, in order to provide a substantially uniform accelerating field in the region between first control grid 20 and screen grid portion 22. The convergent electron lens, comprising third focusing electrode 2I and screen grid portion 22, serves to focus the electron beam in such a way that it is substantially parallel or slightly convergent upon emerging from aperture 24 of the beam directing portion of second accelerating electrode 23.

A second control grid 26 is disposed across electron path I0 beyond aperture 24 at a distance greater than at least one of the transverse dimensions (for example, the width) of that aperture. Second control grid 26 also has a step function type operating characteristic by virtue I of this space relationship between second control grid 26 and aperture 24. Electrons emerging from second control grid 26 are collected by anode 28, which is maintained at a positive operating potential.

In practice, it is preferred to maintain auxiliary electrode I3 and focusing electrodes I4, I9, 2|, and 25 at cathode potential by means of internal conductive connections between these electrodes.

The device of Figure 1 comprises a pair of control grids 20 and 26 arranged in cascade along a single electron path I0. These grids may be compared with a pair of interrupter switches, the passage of current to anode 28 being dependent on both switches being closed. Assuming that the first grid 20 is operated at a suitable fixed bias potential, a sinusoidal input signal applied to the first grid 20 results in a substantially square wave space current within the tube, the conducting and non-conducting portions being equal in length. If a signal of the same frequenc is applied to the second grid 26, space current flows only during those periods when the signals applied to both grids are simultaneously positive. If the two signals are in phase, anode current flows during one-half of each cycle, and the average anode current is one-half of the maximum instantaneous value of space current. If, now, the signal applied to the second grid 26 is shifted 90 in phase with respect to the signal applied to the first grid 20, anode current flows during only one-fourth of each cycle, and the average anode current is one-fourth the maximum value of instantaneous space current. Variations of the phase displacement between the two signals produce corresponding variations in the lengths of the conductive periods, and therefore, in the average anode current. Thus, the average anode current is proportional to the phase displacement between the signals applied to the two control grids 20 and 26. Such a proportionality is exactly what is required for frequency demodulation. Since amplitude limiting is effectively obtained because of the step function characteristics associated with each grid. a tube of the type shown in Figure 1 is particularly adaptable to use as a combined amplitude limiter and frequency demodulator in a frequency modulation radio receiver.

While the various elements are separately recited in the appended claims, it is contemplated that certain groups of electrodes customarily operated at a common potential may be integrall formed, and it is understood that the claims may be interpreted to cover an electron discharge device incorporating such integrally formed electrodes. For example, there is shown in Figure 2 a schematic representation of an electron discharge device which is functionally the same as that shown and described in connection with Figure 1. In the embodiment of Figure 2, in order to facilitate mass production on an economical basis, wing portions I6 of auxiliary electrode I3 and first focusing electrode I4 are integrally formed, as are first accelerating electrode I5 and beam directing portion 23 of the second accelerating electrode. Second focusing electrode I9 and third focusing electrode 2| are also combined in a single structural part. In this manner, the necessity for separate supporting posts 29 is obviated.

There is shown in Figure 3 a schematic circuit diagram of a combined amplitude limiter and frequency demodulator which utilizes a tube constructed in accordance with the schematic representation of Figure 1. Frequency modulated input signals are applied to the first control grid 20 from any suitable source, as for example, the intermediate amplifier of a superheterodyne receiver (not shown), by way of input terminals 30 and 3|. Suitable constant operating bias voltage is supplied by means of a cathode resistor 32 and associated bypass condenser 33 arranged in parallel between cathode II and ground in the customary manner. The first accelerating electrode I5 and the second accelerating electrode comprising screen grid portion 22 and beam directing portion 23 are connected either internally or externally and are in turn connected through a voltage dropping resistor 44 to the positive terminal of a suitable source of positive unidirectional operating potential, here shown as a battery 34, the negative terminal of which source is grounded. Accelerating electrodes I5 and 23 are bypassed to ground by a condenser 45. A parallel resonant circuit 35, comprising an inductor 36 and a condenser 31, is connected between second control grid 26 and ground. It is to be understood that condenser 31 may comprise the distrlbuted capacity of the circuit, and in some cases, there is no necessity for the use of a discrete -capacitive circuit element. An anode load resistor 38 is connected between anode 28 and the positive terminal of battery 34. A pair of output terminals 39 and 40 are connected to anode 28 and to ground respectively. Output terminals 39 and 40 are bypassed for the intermediate frequency by means of a condenser 4|.

In operation, parallel resonant circuit 35 is tuned to the intermediate frequency. As is taught by Zakarias in U. S. Patent No. 2,208,091, a unidirectional space charge coupling exists from input grid 20 to second control grid 26. That is to say, voltage is induced on the second grid 26 by the space current passed by the first grid 20, however, the potential of first control grid 20 is unaffected by any potential variation of second control grid 26. This space charge coupling from first grid 20 to second grid 26 is equivalent phasewise to a unilateral negative capacity; consequently, the voltage induced on the second grid 26 lags the voltage at the first grid 20 by exactly 90 whenever the input signal falls at exactly the frequency to which circuit 35 is tuned. Frequency deviation of the input signal results in a change in the phase displacement between the voltages appearing on the first and second grids 20 and 26, and thus in the average anode current. As a result, the output voltage appearing between terminals 39 and 40 varies in amplitude in accordance with the frequency variation of the input signal applied between terminals 30 and 3|.

The circuit described is substantially unresponsive to amplitude variations of the input 'signal because of the step function type operating characteristics of the control grids. The response to amplitude variations of the input signal is further reduced by the substantially constant amplitude of the quadrature signal, which develops on grid 26 as a result of unilateral space charge coupling from first control grid 20 for all input signal voltages exceeding a certain minimum amplitude.v This stability of the quadrature voltage results from the fact that the space charge which develops in the vicinity of control grid 26 is a function of the space current, and that in a tube constructed in accordance with this invention, the space current varies between zero and a substantially constant intensity.

The demodulator characteristic for the circuit shown and described in connection with Figure 3 is shown graphically in Figure 4 as curve 42. The demodulator characteristic for the well known combination of an amplitude limiter and a conventional double diode phase sensitive discriminator is shown graphically as dotted curve 43, the horizontal axis of curve 43 having been displaced for the purpose of facilitating comparison between the two systems. The output of the circuit of Figure 3 is similar to that of the double diode phase sensitive discriminator within the I linear region, although the characteristic peaks cuit shown and described in connection with Figure 3 provides a wider linear region of operation than does the conventional circuit, thus permitting improved-tuning and greater output.

The electron gun used in the electron discharge device shown schematically in Figures 1 and 2, comprising cathode H, auxiliary electrode I3, focusing electrode [4, and accelerating electrode l5, provides a well defined beam while affording a particularly high perveance. By providing conductive connections between cathode ll, auxiliary electrode l3, and focusing electrode I4, such well defined beam is obtained with the application of a single positive operating potential to accelerating electrode l5, there being no necessity for the use of adjustable auxiliary operating potentials for focusing purposes. Thus an electron gun of this type may also find utility in velocity modulation tubes, traveling wave tubes, and the like, wherein a relatively large space current is desired with relatively low operating potentials.

While the invention has been shown and described in connection with certain specific embodiments thereof, it is to be understood that numerous variations and modifications may be made. It is therefore contemplated in the appended claims to cover all such variations and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An electron discharge device comprising an electron gun including: a cathode having a, substantially plane emitting surface; an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface: a focusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface; and an accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture the boundaries of which extend toward said cathode and terminate at a distance from those boundaries nearest said cathode of the aperture of said focusing electrode which does not exceed a small fraction of the transverse dimensions of the aperture of said accelerating electrode.

2. An electron discharge device comprising an electron gun including: a cathode having a substantially plane emitting surface; an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface; a f0- cusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface; and an accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture bounded by at least one flange extending toward said cathode and terminating at a distance from those boundaries nearest said cathode of the aperture of said focusing electrode which does not exceed a small'fraction of the transverse dimensions of the aperture of said accelerating electrode.

3. An electron discharge device comprising an electron gun including: a cathode having a substantially plane emitting surface; an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface; a focusing electrodespaced from said cathode and having an aperture disposed opposite said emittin; surface; and an accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture bounded by at least one flange extending toward said cathode and into the aperture of said focusing electrode, and terminating at a distance from those boundaries, nearest said cathode of the aperture of said focusing electrode which does not exceed a small fraction of the transverse dimensions of the aperture of said accelerating electrode.

4. An electron discharge device comprising an electron gun including: a cathode having a substantially plane emitting surface; an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface; a focusing electrode spaced from said cathode and having a slot disposed opposite said emitting surface; and an accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having a slot bounded by a pair of opposed lips extending toward said cathode and terminating at a distance from those boundaries nearest said cathode of the slot of said focusing electrode which does not exceed a small fraction of the width of the slot of said accelerating electrode.

5. An electron discharge device comprising an electron gun including: a cathode having a substantially plane emitting surface; an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface; a, focusing electrode spaced from said cathode and having a slot disposed opposite said emitting surface; and an accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having a slot bounded by a pair of opposed lips extending toward said cathode and into the slot of said focusing electrode and terminating at a distance from those boundaries, nearest said cathode of the slot of said focusing electrode which does not exceed a small fraction of the width of the slot of said accelerating electrode.

6. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a, substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having an aperture disposed opposite saidemitting surface, and a first accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture the boundaries of which extend'toward said cathode and terminate at a distance from the boundaries of the aperture of said focusing electrode which does not exceed a small fraction of the transverse dimensions of the aperture of said first accelerating electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said first accelerating electrode; a, convergent electron lens; a second accelerating electrode including a part of said electron lens and a beam directing portion having an aperture; 3, second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said beam directing portion; and an anode.

7. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substan- 10 tially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface, and a first accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture bounded by at least one flange extending toward said cathode and terminating at a distance from the boundaries of the aperture of said focusing electrode which does not exceed a small fraction of the transverse dimensions of the aperture of said first accelerating electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said first accelerating electrode; a convergent electron lens; a second accelerating electrode including a part of said electron lens and having an aperture; a second control grid spaced from said second accelerating electrode by a, distance greater than at least one of the transverse dimensions of the aperture of said second accelerating electrode; and an anode.

8. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface, and a first accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture bounded by at least one flange extending toward said cathode and terminating at a distance from the boundaries of the aperture of said focusing electrode which does not exceed a small fraction of the transverse dimensions of the aperture of said first accelerating electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said first accelerating electrode; a convergent electron lens comprising a screen grid; a second accelerating electrode including said screen grid and a beam directing portion having an aperture; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said beam directing portion; and an anode.

9. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron'gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface, and a first accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture bounded by at least one flange extending toward said cathode and terminating at a distance from the boundaries of the aperture of said focusing electrode which does not exceed a small fraction of the transverse dimensions of the aperture of said first accelerating elec- 11 trode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said first accelerating electrode and having a contour which is substantially convex towards said first accelerating electrode; a convergent electron lens comprising a screen grid having a contour substantially similar to that of said first control grid; a second accelerating electrode including said screen grid and a beam directing portion having an aperture; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said beam directing portion; and an anode.

10. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having a slot disposed opposite said emitting surface, and a first accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having a slot bounded by a pair of opposed lips extending toward said cathode and terminating at a distance from the boundaries of the slot of said focusing electrode which does not exceed a small fraction of the width of the slot of said first accelerating electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the slot of said first accelerating electrode and having a contour which is substantially convex towards said first accelerating electrode; a convergent electron lens comprising a screen grid having a contour substantially similar to that of said first control grid; a second accelerating electrode including said screen grid and a beam directing portion having a slot; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the slot of said beam directing portion; and an anode.

11. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portionof which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface, and a first accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture bounded by at least one flange extending toward said cathode and into the aperture of said focusing electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said first accelerating electrode; a convergent electron lens comprising a screen grid;'a second accelerating electrode including said screen grid and having an aperture; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said second accelerating electrode; and an anode.

12. An electron discharge device comprising a plurality of elements disposed -in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary'electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface, and a first accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture bounded by at least one fiange extending toward said cathode and into the aperture of said focusing electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said first accelerating electrode and having a contour which is substantially convex toward said first accelerating electrode; a convergent electron lens comprising a screen grid having a contour substantially similar to that of said first control grid; a second accelerating electrode including said screen grid and a beam directing portion having an aperture; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said beam directing portion; and an anode having a contour substantially similar to that of said second control 13. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, a auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a first focusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface, and a first accelerating electrode spaced from said first focusing electrode on the side thereof remote from said cathode and having an aperture bounded by at least one flange extending toward said cathode and into the aperture of said first focusing electrode; a second focusing electrode having an aperture materially larger than that of said first accelerating electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said first accelerating electrode and having a contour substantially convex toward said first accelerating electrode; a convergent electron lens comprising a third focusing electrode followed by a screen grid having a contour substantially similar to that of said first control grid; a second accelerating electrode including said screen grid and a beam directing portion having an aperture larger than that of said first accelerating electrode; a fourth focusing electrode having an aperture materially larger than that of said beam directing portion; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the an anode having a contour substantially similar to that of said second control grid.

path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface. a first focusing electrode spaced from said cath ode and having an aperture disposed opposite said emitting surface, and a first accelerating electrode spaced from said first focusing electrode on the side thereof remote from said cathode and having an aperture the boundaries of which extend toward said cathode and into the aperture of said first focusing electrode; a second focusing electrode having an aperture materially larger than that of said first accelerating electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said first accelerating electrode and having a contour substantially convex toward said first accelerating electrode; a convergent electron lens comprising a third focusing electrode followed by a screen grid having a contour substantially similar to that of said first control grid; a second accelerating electrode including said screen grid and a beam directing portion having an aperture larger than that of said first accelerating electrode; a fourth focusing electrode having an aperture materially larger than that of said beam directing portion; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said beam directing portion;

and an anode having a contour substantially similar to that of second control grid.

15. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a first fcusing electrode spaced from said cathode and having a slot disposed opposite said emitting surface, and a first accelerating electrode spaced from said first focusing electrode on the side thereof remote from said cathode and having a slot bounded by a pair of opposed lips extending toward said cathode and terminating at a distance from the boundaries of the slot of said first focusing electrode which does not exceed a small fraction of the transverse dimensions of the slot of said first accelerating electrode; a second focusing electrode having a slot materially larger than that of said first accelerating electrode: a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the slot of said first accelerating electrode and having a contour substantially convex toward said first accelerating electrode; a convergent electron lens comprising a third focusing electrode followed by a screen grid having a contour substantially similar to that of said first control grid; a second accelerating electrode including said screen grid and a beam directing portion having a slot larger than that of said first accelerating electrode; a fourth focusing electrode having a slot materially larger than that of said beam directing portion; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said beam directing portion; and an 14 anode having a contour substantially similar to that of said second control grid.

16. An electron discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface. a first focusing electrode spaced from said cathode and having a slot disposed opposite said emitting surface, and a first accelerating electrode spaced from said first focusing electrode on the side thereof remote from said cathode and having a slot bounded by a pair of opposed lips extending toward said cathode and into the slot of said first focusing electrode: a second focusing electrode having a slot materially larger than that of said first accelerating electrode; a first control grid spaced from said first accelerating electrode by a distance greater than at least one of the transverse dimensions of the slot of said first accelerating electrode and having a contour substantially convex toward said first accelerating electrode; a convergent electron lens comprising a third focusing electrode followed by a screen grid having a contour substantially similar to that of said first control grid; a second accelerating electrode in cluding said screen grid and a beam directing portion having an aperture larger than that of said first accelerating electrode; a fourth focusing electrode having a slot materially larger than that of said beam directing portion; a second control grid spaced from said second accelerating electrode by a distance greater than at least one of the transverse dimensions of the aperture of said beam directing portion; and an anode having a contour substantially similar to that of said second control grid.

17. An electron-discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having an aperture disposed opposite said emitting surface, and an accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having an aperture the boundaries of which extend toward said cathode and terminate at a distance from the boundaries of the aperture of said focusing electrode which does not exceed a small fraction of the transverse dimensions of the aperture of said accelerating electrode; a control grid spaced from said accelerating electrode by a distance greater than at least one of the transverse dimen sions of the aperture of said accelerating electrode; and a convergent electron lens for refocusing electrons passed by said control grid.

18. An electron-discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having a slot disposed opposite said emitting surface, and an accelerating electrode spaced from said tron lens for refocusing electrons passed by said control grid.

19. An electron-discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having a slot disposed opposite said emitting surface, and an accelerating electrode spaced from said focusing electrode on the side thereof remote from said cathode and having a slot bounded by a pair of opposed lips extended toward said cathode and terminating at a distance from the boundaries of the slot of said focusing electrode which does not exceed a small fraction of the width of the 'slot of said accelerating electrode; a control grid spaced from said accelerating electrode by a distance greater than at least one of the transverse dimensions of the slot of said accelerating electrode; and a convergent 35 2,139,678

electron lens comprising a screen grid for refocusing electrons passed by said control grid.

20. An electron-discharge device comprising a plurality of elements disposed in substantially symmetrical relation across a common electron path and including in the order named: an electron gun including a cathode having a substantially plane emitting surface, an auxiliary electrode at least a portion of which is substantially coplanar with said emitting surface, a focusing electrode spaced from said cathode and having a slot disposed opposite said emitting surface, and

an accelerating electrode spaced from said fov cusing electrode on the side thereof remote from said cathode and having a slot bounded by a pair of opposed lips extending toward said cathode and terminating at a distance from the boundaries of the slot of said focusing electrode which does not exceed a small fraction of the width of the slot of said accelerating electrode; a control grid spaced from said accelerating electrode by a distance greater than at least one of the transverse dimensions of the slot of said accelerating electrode; and a convergent electron lens comprising a second focusing electrode followed by a screen grid for refocusing electrons passed by said control grid.

ROBERT ADLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Glass Dec. 13, 1938 2,268,195

Winans Dec. 30, 1941 

